Signal receiver for carrier wave systems



Aug. 13,1940. sKlLLMAN I 2,210,957

SIGNAL RECEIVER FOR CARRIER WAVE SYSTEMS Filed Dec. 1'7, 1938 1 1/ If! A :I- -1 ZZZ:

Patented Aug. 13, 1940 UNITED STATES SIGNAL RECEIVER FOR CARRIER WAVE SYSTEMS Thomas Samuel Skillman, Eindhoven, bletherlands, assignor, by mesne assignments, to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application December 1'1, 1938, Serial No. 246,457 In Germany December 27, 1937 2' Claims.

This invention relates to carrier-telephony systems especially multichannel systems in which the signals, such as calling currents or dialling impulses are transmitted by the emission of the 5 carrier, which is suppressed during the transmission of the conversation, or by a signal current lying in the side-band.

;To select the signal .at the receiving station a signal receiver is provided which comprises a filter or an oscillatory circuit tuned to the carrier-frequency or to the frequency of the signalcurrent lying in the side-band. After selection the signal is supplied to a rectifier and rectified. The rectified current controls a relay which"op-.

crates the signalling circuit. Usually the recti-, fied current is too weak directly to operate the relay, so that an amplifier must be interposed. However, this additional amplifier renders the installation more expensive.

This amplifier can be dispensed with if, ac-

cording to the invention, the relay operating the signal-current circuit is interposed in the anode circuit of alow-frequency amplifying tube in the 'receiving channel which tube is provided for amplification of the demodulated conversation, the grid voltage of said tube being controlled by the rectified signal current.

One form of construction of a signal receiver according to the invention is represented in the' drawing.

' The conversation coming in over the line L1 is supplied in the usual manner through a differential transformer T with line balance N to .a modulator M where it is modulated on the carrier p1 produced in the generator G1. The modulator is constructed in a known manner so that the carrier is suppressed and only the two side-bands appear in its output circuit. One of these side-bands is suppressed in the band-pass 40 filter BF1 and the other side-band is supplied to the line L2. Similar transmitting channels may be connected to this line. Signalling is effected by means of a switch S which controls a relay switch l-2 connected to the carriergenerator. Thus, by an opening and closing the switch S signal impulses of carrier frequency in can be sent-on the line L2.

The side-band carrying the conversation coming in over the receiving line L3 is selected by means of a filter BFz, and demodulated in the demodulator DM while adding the carrier p2 of the generator G11 and after amplification in ;the amplifying tube V1 supplied as a low-frequency conversation to the line L1.

Signal impulses of carrier frequency p: coming in over the line In are supplied to a tube V2. The anode-circuit of this tube has coupled to it a mixing circuit comprising a rectifier F1, an

auxiliary generator H having a frequency p: and the primary winding of a transformer T1. An oscillatory circuit LC tuned to the difference frequency pa-pz is connected to the secondary winding of the said transformer. The voltage 5 set up at the coil L is rectified by means of a second rectifier F2 as the result of which a direct voltage drop is produced across the resistance W. This resistance W is'connected in the grid circuit of the amplifying tube V1 provided for. the amplification of the demodulated received side band. The anode-circuit of said tube V1 comprises a relay R2 which operates the signal current circuit I. Upon reception of signal impulses such a voltage drop is produced at the resistance W in the grid circuit of the amplifying tube V1 that the anode current of the tube V1 is entirely or partly suppressed, the relay R2 is caused to respond and the signals are transmitted to the signalling circuit J. I

In the above example the signals are transmitted by transmission of the carrier-wave which is suppressed during the transmission of the conversation. However, it will be appreciated that the invention also applies to carrier systems, wherein the signals are transmitted by means of a signal-current lying in the side-band.

What I claim is:

1. In a carrier-telephony signal receiver adapted to receive signal currents which are transmitted by the emission of the carrier, means for filtering the signal currents received, means for rectifying the filtered currents, means for amplifying the speech currents including a lowfrequency amplifying tube inthe receiving channel and having a grid, a plate circuit for said tube, means for controlling the grid bias of. said tube by the rectified signal currents, a signallin circuit, and a relay connected to control sail signalling circuit and controlled by the plate current of said plate circuit.

2. In a carrier-telephony signal receiver adapted to receive signal currents which are transmitted by the emission of the carrier,. means for amplifying the speech currents in-v cluding a low-frequency amplifying tube in the receiving channel and having a grid, a plate circult for said tube, a signalling circuit, a relay connected to control said signalling circuit and controlled by the plate current of said tube. means for, superposlng an auxiliary frequency on the signal current frequency to produce a 1 difference frequency, means for rectifying the difference frequency, and means for controlling the grid voltage of said tube by the rectified diflerence frequency.

THOMAS SAMUEL SULLMAN. 

